Refining fatty oils



Apnl 25, 1950 e. H. PALMER REFINING FATTY OILS Filed Feb. 5, 1948 3 Sheets-Sheet 1 on uzo- 22:20.55.

IN VEN TOR.

April 25, 1950 Filed Feb. 5. 1948 G. H. PALMER REFINING FATTY OILS 3 SheetsSheet .3

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Patented Apr. 25, 1950 BEFININ G FATTY OILS George H. Palmer, Fanwood, N. J., assignor to The M. W. Kellogg Company, Jersey City, N. L, a corporation of Delaware Application February 5, 1948, Serial No. 6,459

This invention relates to improvements in the refining and fractionation of fatty oils, 1. e. oils consisting principally of glycerol esters of fatty acids, such as cottonseed oil, cocoanut oil, linseed oil, soybean oil, palm oil, peanut oil, sardine body oil, cod liver oil, menhaden oil, and whale oil.

It has, been suggested previously to fractionate fatty oils by contacting the oil with a, low-boiling solvent at temperatures in a temperature range, near the critical temperature of the solvent, in which the solubility of the oil and solvent decreases with rising temperature. This temperature range lies above the temperature of maximum solubility which is ordinarily not more than about 100 F. below the critical temperature of the solvent, and extends to a few degrees above the critical temperature of the solvent.

In this temperature range solubility is greatly affected by conditions which affect the density of the solvent. The condition of the solvent in this temperature range, in which its solvent power is greatly affected by slight changes in temperature and/or pressure, has been designated arbi trarily as the paracritical state." In this condition the pressure is always maintained sufllciently high to keep the solvent substantially entirely in liquid condition, and the degree of solubility of the oil and the solvent is afiected by the temperature, the relative quantities of solvent and oil employed, the pressure, and the nature of the solvent.

This invention relates to an improved method of fractionating fatty oils by means of a relatively volatile, i. e. relatively low-boiling, solvent while the solvent is in the paracritical state.

Relatively volatile solvents are employed for the reason that the solvents which are partially miscible with the oil while in the paracritical state ordinarily are those having critical temperatures no higher than 450 F., and it is desirable to avoid operating temperatures which might produce some thermal effect on the oil being treated.

In carrying out the improved fractionation process any fluid may be employed which is partially miscible, while in its paracritical state, with the oil to be treated, and does not react chemically with the oil. Such solvents include low-boiling hydrocarbons, such as methane, ethane, propane, the butanes, the pentanes, and

the corresponding, olefins, as well as mixtures thereof, such as a mixture of methane and normal butane, or a mixture of ethane and propane. Other agents include organic compounds such as halogenated hydrocarbons, including dichlor- 16 Claims. (CI. 260-4285) difluor methane and methyl fluoride. Still other solvents which may be used are dimethyl ether, methyl ethyl ether, carbon dioxide, and ammonia.

The low-boiling normally gaseous parafln hydrocarbons are preferred solvents because of their lower cost and relative inertness, and because they are miscible with most fatty oils to the desired degree. Propane is ordinarily preferred in carrying out the process but the other low-boiling hydrocarbons may be preferred in the treatment of certain oils. It may be advantageous to modify the propane, or other hydrocarbon solvent employed, by the incorporation of a small amount of a diiferent solvent. Furthermore, the employment of relatively impure materials, such as commercial propane containing small quantities of other hydrocarbons, principally ethane, is within the scope of the invention.

In accordance with the improved process of this invention the fatty oil is refined by fractionation treatment which separates the oil into three or more separate fractions having distinctly different properties. This treatment is carried out in at least two separate contacting zones.

It is a principal object of the invention to provide a process for continuously fractionating a fatty oil into three or more fractions in at least two separate contacting zones by means of circulating solvent while evaporating and condensing a smaller quantity of solvent than in previous processes for eifecting the same fractionation. It is a further object to provide a continuous process for fractionating a fatty oil into three or more fractions in two or more separate contactingzones without evaporation of the solvent except for the purpose of separating the solvent from product fractions. Other objects of the invention will be apparent from the following more deified description of the invention.

The invention will be described in detail with reference to the accompanying drawings, in which (1) Figure l is a diagrammatic representation in elevation of an arrangement of apparatus for carrying out one embodiment of the improved process, with certain modifications,

(2) Figure 2 is a diagrammatic representation in elevation of an arrangement of apparatus for carrying out an embodiment of the invention in which the oil is fractionated into four product fractions, and

(3) Figure 3 is a diagrammatic representation in elevation-of an arrangement of apparatus for 66 effecting fractionation of a fatty oil into four fractions by a flow arrangement difierent from a that of Figure 2.

Fig. 1 illustrates an arrangement of apparatus for fractionatin a fatty oil into three product fractions, in accordance with the improved process of this invention. This operation produces a relatively large intermediate fraction which is light in color and substantially neutral, a relatively small first rafiinate fraction comprising a concentration of the color 'bodies of the fatty oil, and a final extract fraction which is a concentration of fatty acids and other highly soluble components of the fatty oil. The relatively large intermediate fraction is a substanhigh concentration of lecithin and other phosphatides, and the final extract fraction contains, in addition to the fatty acids, a relatively high concentration of tocopherols and sterols. Each of the relatively small fractions represents a concentration of valuable components and may be converted into highly desirable products by further treatment.

In the process of Fig. 1, the first raflinate fraction and the final extract fraction are each ordinarily limited to a quantity equivalent to less than 10' per cent (by weight) of the fatty oil being treated. Preferably the first rafiinate fraction constitutes no more than 5 per cent of the fatty oil, while the final extract fraction is limited to 2 per cent or less of the fatty oil. For example, in the refining of soybean oil the first rafiinate fraction preferably is limited to 2 per cent or less of the fatty oil, while the final extract fraction is about 1 or 2 per cent of the fatty oil.

In the process illustrated in Fig. 1, a fatty oil is treated in an extraction zone provided by fractionating tower 10 to separate the first raffinate fraction, which is withdrawn from the bottom of tower i0. Extract oil, whose most soluble components comprise the most soluble components of the fatty oil, is withdrawn from the top of tower 10 as a part of the extract phase and further treated in a separate fractionating zone in tower H to separate such extract oil into a final extract fraction and the relatively large intermediate fraction of the fatty oil.

Tower II is arranged and equipped to provide intimate contact of the extract oil and solvent under conditions which effect close fractionation of the oil, i. e. concentration in the extract of components undesired in the intermediate product, or desired to be concentrated in the final extract product. To this end, fractionating tower vertically and is provided with contact means, such as trays, bafiles or packing, to efiect intimate contact of counter-flowing liquid phases. Tower I! also is provided with means for effecting extensive refluxing of the tower with extract oil. Such refluxing is effected by means of heating coils 12, which heat the extract phase as it flows up the tower to precipitate oil from the H is substantially elongated d extract phase, or it may be provided by separating a portion of extract 011 from the extract phase and returning it to the upper part of tower I l, i. e. external refluxing.

The initial extraction treatment of the fatty oil to separate a first rafiinate, containin a concentration of the color bodies, may be carried out under any suitable conditions, but it is preferred to effect substantially complete removal of color bodies and a high concentration of other components of lesser solubility in the first rafiinate product by subjecting the fatty oil initially to fractionation treatment under conditions substantially equivalent to, those provided by tower H. Consequently, tower I0 is generally similar to tower II in the provision of the various means for achieving close fractionation, i. e. substantial segregation of the less soluble components of the fatty oil in the raflinate, and vice versa.

In the normal operation of fractionating tower I a solvent stream consisting essentially of propane or other suitable solvent is introduced into the tower at a point near the bottom thereof, through line [5. The solvent stream is heated or cooled to the temperature desired in the bot-' tom of the tower, by means indicated at It, and line i5 is provided with a pump I! to overcome the pressure maintained on tower III. A stream'of the fatty oil to be treated, such as soybean oil, is introduced into tower I0 at one or more intermediate points, as through line 18. The operating conditions imposed on tower I0 are such that, at equilibrium conditions, the fatty oil is only partly soluble in theupfiowing sol vent stream. As a result of the difference in gravity between the undissolved oil phase and the solvent phase, the undissolved oil phase fiows downwardly in counter-current contact with the upfiowing solvent phase. The solvent phase fiows upwardly toward an overhead drawoff line at 19 while the oil, or lower, or rafiinate, phase flows downwardly toward a bottoms drawoff line at 20. The upfiowing solvent phase contains all but a small proportion of the solvent introduced from line l5 and a portion of the fatty oil. This phase also may be designated as the propane phase, or upper phase, or extract phase. The lower, or oil phase contains only a small proportion of the solvent and a portion of the oil in a solventzoil ratio much lower than that existing in the solvent phase.

The volumetric ratio of solvent and oil introduced into tower I0 should be not lower than about 6:1 and preferably should be at least 10:1, for example, 15:1 to 3021, or higher. Tower I0 is maintained under suificient pressure to maintain the solvent substantially entirely in liquid condition. The operation essentially requires contact of the liquid solvent phase with the liquid oil phase, but the formation of a small quantity of solvent vapor is not objectionable so long as it does not interfere with the flow of the liquid phases in counter-current contact through and out of the tower. Since the operation of tower Ill essentially involves withdrawing the major portion of the fatty oil in the extract phase, the maximum temperature in the tower ordinarily is substantially lower than the critical temperature of the solvent. The critical temperature of propane is 206.3 F., whereas the critical pressure is 617.4 p. s. 1. Consequently, when using propane as the solvent a maximum operating pressure of 400-700 p. s. i. is satisfactory.

solvent contained in the extract phase.

Tower is divided into two zones by the introduction of the fatty oil from line 18 at an intermediate point. The upper zone, lying above this point, is the rectification zone in which the operation of the tower .is directed substantially entirely to achieving the desired degree of fractionation of the constituents of the -fatty oil which are absorbed in the solvent phase at lower points in the tower. The lower zone, lying below the oil charge point, is primarily a stripping zone in which the undissolved fatty oil and oil precipitated in the rectification zone are sub- Jected to the stripping action of the upfiowing stream of solvent, to dissolve in the solvent phase all constituents of the fatty oil except those which it is desired to include in the first rafiinate fraction, to be withdrawn through line 20.

Rectification may be effected by heating the solvent phase, as it flows upwardly past the oil oil and solvent, and since the solvent phase is saturated with oil at the lower temperature, the heating of the solvent phase to a higher temperature as it flows up the tower results in a decrease in density of the solvent and a corresponding precipitation of a part of the oil previously dissolved. This precipitated oil "forms a new raflinate phase which flows down the tower in counter-current contact with the solvent phase, to effect further rectification of the oil.

Any suitable means may be employed for heating the solvent phase as it flows up the tower, but ordinarily this is efiected by heating coils I4 which are located at suitable intervals in that portion of the tower in which it is desired to maintain a temperature gradient. The temperature differential between the top and bottom of tower It! may vary from 1 F. to 60 F.

-The temperature gradient employed may be concentrated entirely between the oil charge point and the top of the tower or it may extend from top to bottom of the tower. Conveniently, a relatively small temperature gradient may be imposed on the stripping zone, while a larger temperature gradient is imposed on the rectification zone.

Alternative to the maintenance of a temperature gradient in tower ID, or in combination with that method, the tower may be refluxed by the return to the top of the tower of a portion of the extract oil. According'to this method all, or a portion, of the extract phase withdrawn through line i9 is diverted through line 2| which connects with a separator 22. The pressure on the extract phase flowing through line 2| is substantially reduced by means of valve 23 to effect vaporization of the greater part of the To assist in this operation heating means 24 may be provided in line 2|. In vessel 22 the liquids and vapors are separated and the solvent vapors pass overhead through line 25, which connects with solvent storage vessel 26. A cooler 21 is provided in line 25 to condense the solvent vapors.

- .The removal of solvent from the extract phase in vessel 22 may not be complete, and it is preferable not to remove the solvent completely since this requires excessive reduction in pressure at 23 or excessive heating, and since the return of a small part of the solvent in the reflux liquid does not interfere with the operation of tower l0. For example, if tower I0 is operated with a propane solvent at about 600 p. s. i., the pressure may be reduced at 23 to about 200 p. s. i., heat being supplied at 24 to replace heat of evaporation. This effects a sufficient removal of solvent and simplifies condensation of the solvent vapors at 21.

The reflux liquid, comprising extract oil and a small amount of the solvent, is collected in the bottom of vessel 22 and withdrawn therefrom through line 28 by means of pump 29. All, or a portion, of this oil is diverted from line 28 through line 30 for return to the top of tower The refluxing of tower III by the return of extract oil through line 30 is not essential to the operation of tower It as reflux oil from other sources may be introduced into the top of tower II). For example, a suitable portion of raflinate phase produced in tower ll may be collected and returned to the top of tower I 0, by means not shown. Moreover it may be desirable to avoid all external refluxing, relying only on the refluxing provided by the temperature gradient to effect the desired rectification of the extract.

Conditions of temperature and pressure in tower H! are regulated to distribute to the ratfinate phase which collects in the bottom of tower to, only a minor proportion of the fatty oil. In the two-zone system of operation illustrated by Fig. 1 it is desirable ordinarily to limit the proportion of the oil in the railinate phase withdrawn through line 20 to the maximum proportion which is necessary to remove the color bodies and other relatively insoluble constituents from the extract. This will require ordinarily a railinate containing not more than about 5 per cent of the fatty oil and, in the treatment of certain oils, such as soybean oil, this proportion may be 2 per cent or less. However, it may be desirable to operate tower I to produce a raflinate containing a substantially larger, although minor, proportion of the fatty oil. For example, it may be desirable to operate tower ID to produce a raflinate oil representing a concentration of the more unsaturated glyceride components of the fatty oil for use as a drying oil. For this purpose it may be desirable to produce a raftinate oil in tower l0 representing 15 percent, or more, of the fatty oil charged to tower l0. Ordinarily, however, the production of such a drying oil fraction is effected in a three-zone arrangement, to be described below.

The exact operating conditions selected for tower l0 depend upon the character of the oil being treated and the proportions of oil and solvent employed, as well as the desired distribution of the oil between the raffinate and extract. The smaller the proportion of the fatty oil desired in the ramnate, the lower will be the temperature desired in the bottom of the tower. 0n the other hand, a relatively high ratio of solvent to oil charged to tower l0 requires a higher bottom temperature in the tower toaaoasss rectification, the tower temperature necessarily must be substantially lower than in the absence of such external rectification, in order to incorporate the desired proportion of the fatty oil in the rafiinate. In general, the bottom temperature controls the amount of oil rejected to the rafl'lnate phase for withdrawal as bottoms, while the top temperature controls the amount of oil withdrawn overhead to produce the extract oil to be withdrawn and reflux oil to be returned to the tower. In the treatment of soybean oil to remove a small rafiinate as a concentration of color bodies the temperature in the bottom of tower I will fall within the range of 140-190" F., while the temperature at the top of the tower will be in the range of 150-200 F.

The extract oil from tower I0 is further fractionated in tower II to separate it into a raflinate comprising a major portion of the oil charged to tower II, and an extract containing a portion of the oil charged to tower II. In accordance with a preferred modification of the process of Fig. 1 the portion of the extract phase withdrawn through line I9, and not diverted through line 2| for production of reflux liquid, is passed on through control valve 3| to an intermediate point of tower II. Tower II is similar to tower I0 in construction and in the provision of means for effecting contact of counter-flowing liquid phases, heating the extract phase, and external refluxing. A solvent stream is drawn from reservoir 26 by means of line 32 and introduced into tower II at a low point. Line 32 is provided with pump 33 and temperature control means 34. Tower II is operated at somewhat higher temperatures than is tower I0, as it is desired to include in the final extract phase a substantially smaller proportion of the fatty oil than has previously been dissolved in tower I0. Tower II preferably is operated with a temperature gradient, and under these conditions the bottom temperature will be in the range 160-195 F., while the top temperature is in the range 165-210 F., although in certain cases an even higher top temperature may be imposed on tower II. I

Heating means 35 are provided in line I9 to regulate the temperature of the solvent phase from tower Ill introduced into tower II through line I9. The temperature of this liquid may be brought to-the temperature desired to be maintained in tower II at the point of introduction, or the liquid from line I9 may be heated to an even higher temperature to assist in heating the solvent-phase flowing upwardly in tower II toward the outlet of line I9.

Tower II conveniently is maintained under a sufficiently lower pressure than tower III in order to permit flowing the solvent phase from tower I0 directly through line I9 into tower II. Preferably tower I I is maintained substantially at the pressure required to prevent substantial vaporization of the solvent in the tower. This requires maintaining tower I0 under a pressure substantially higher than the minimum required to maintain liquid conditions, since tower I0 is at a lower temperature than tower I I. However,

J of tower II it is advantageous to Provide rectifl-- cation by imposing a temperature gradient on the tower, while limiting external refluxing to the minimum. Furthermore, the percentage of the oil in the tower which is permitted to remain in the final extract solution is relatively small, whereby it may be necessary to impose a relatively high temperature at the top of the tower. Consequently, the temperatures in tower II may extend into the region in which the density of the solvent is greatly affected by variations in pressure, and in which the change in density of the solvent produced by a change in the temperature is at a maximum at the lowest pressure necessary to prevent substantial vaporization of the solvent.

Operating conditions in tower II are adjusted to form a secondary rafiinate phase, in the bot.- tom of the tower, which contains oil equivalent to a major proportion of the oil charged'to the tower through line I9. For example, in the treatment of soybean oil by the two-zone system of operation of Fig. 1, the oil charged to tower II may be distributed to the secondary raffinate in the bottom of the tower in an amount equivalent to approximately 90 per cent of the oil charged to tower I I and equivalent to a major proportion of the oil charged to the system through line I8. For example, when tower II is operated to produce a first raffinate product, to be withdrawn through line 20, equivalent to less than 10 per cent of the fatty oil introduced through line I8, the second rafiinate product accumulated in the bottom of tower I I may contain oil equivalent to at least per cent of the fatty oil from line I8. Ordinarily in the refining of soybean oil this twozone process will involve distributing not more than 5 per cent of the fatty oil to the first rafiinate product and at least 93 per cent to the second raiiinate product. In accordance with one specific embodiment of the invention as applied to treatment of soybean oil, the first railinate product withdrawn through line 20 may be limited to 2 per cent or less, while the second raflinate product, collected in the bottom of tower II, may comprise 96 per cent or more of the fatty oil introduced into the system through line I8.

The solvent introduced into the bottom of tower II from line 32 functions principally in that tower to strip from the lower phase flowing down the tower such components of the oil as are undesired in the second rafiinate product, and include these undesired components in the final extract product, along with other relatively soluble components of the oil which may be desired in the flnal extract product. Ordinarily solvent should be introduced into tower II from line 32 in a volumetric ratio of solvent from line 32 to oil introduced from line I9 of at least 6:1, and preferably at least 10:1.

The final extract phase flows out of the top of tower I I through line 36 to a separating vessel 31. The pressure is reduced substantially at valve 38 in line 36 to permit evaporation of at least the greater part of the solvent. To assist this operation heat is applied at 39. Solvent vaporized in this way is separated from the remaining liquid in vessel 31 and is withdrawn overhead for recirculation in the system through line 40, which connects with line 25. The liquid collected in the bottom of vessel 31 is withdrawn through line 4| for recovery and further treatment of the oil product fraction contained therein. If necessary, a portion of this liquid may be returned as reflux liquid to the top of tower II detail below.

with line 40. The liquid separated in the bottom of vessel 45 is withdrawn through line 49 for further treatment and recovery of the oil product fraction contained therein. I

According'to the preferred modification oi the process of Fig. 1, as described above, the extract phase from the top of tower in is passed to tower ii through line I9 without the separation of any df the solvent contained therein except for the production of reflux liquid in tower i0. Preferably it is desired to avoid evanorationof solvent from the extract phase of tower I even to this extent, since it is possible to provide refluxing of tower In by means of a temperature gradient in the tower or by means of reflux liquid obtained from some other external source, as mentioned above. It is advanta eous to introduce into tower II as much as posible of the solvent contained in the extract phase from tower M. One advanta e is that fractionation of the oil in towe ii a pears to be assisted bv the presence of the propane accom'oanving the oil charged from line l9. Another advantage will be described in more Nevertheless, the process includes, as one modification. the substantial se aration of solvent at 22 from all or a sub tantial portion of the extract oil transferred from tower ill to tower II. For this purpose line 28 connects with line i 9, as shown, whereby oil containing a re atively small amount of so vent in adm xture therewith may be transferred from ves el 22 to tower II for further fractionating treatment.

.In accordance with a further modification of the process of Fig. 1. the extractphase li uid flowing through line I!) may be treated to effect a preliminar Sena-ration thereof into separate liquid phases which are separately introduced into tower II at different points. In this modification extract solution flowing through line I9 is diverted therefrom throu h line 50, which connects with vessel 5!. Heating means 52 are interposed in line 50 to heat the extract solution flowing through line 50 to a substantia ly hi her temperature to precipitate a separate liquid phase. settle in vessel 5| to form two separate phases. The upper phase, which now contains a smaller amount of oil, is withdrawn through line 53- and introduced into tower II at a point which may be somewhat below the connection of line 19 with tower II. The lower phase liquid in vessel 5| contains much less solvent than was present in the extract solution in line l9. This liquid is withdrawn through line 54, which connects with line i9, whereby this liquid is introduced into tower Ii at a point which may be substantially above the point of introduction of the upper phase material from vessel 5|. Cooling means 55 and 56 are provided in lines 54 and 53 to adjust the temperatures of these liquids to those at which they are desired to be introduced into tower II. In this modificatiomall, or substantially all, of the extract solution from line I9 is The resulting mixture is permitted to 10 thus diverted through line 50 by suitable manipulation of valve 51 in line and valve 58 in line l9. The phases separated in vessel'il are thus introduced into tower Ii when the extract phase is heated, at 52, to a temperature sufficiently high to precipitate all but a small proportion of the oil. Alternatively, a smaller proportion of the oil may be precipitated and the lower phase liquid from the bottom of vessel-5| may then be introduced into tower H at a lower point than the point of introduction of the upper phase material from vessel 5!.

In accordance with the improved process of this invention the stream of solvent for use in tower I0 is provided by continuously diverting a portion of the final extract phase flowing from the top of tower ll through line 36. For this purpose line i5 is provided to connect line 38 with the lower part of tower I 0. Since the temperature desired in the bottom of tower l0 ordinarily is substantially lowerthan the temperature at which the final extract phase emerges from tower ll, cooling means are provided at IS in line 50 to cool the final extract phase flowing therethrough to the temperature desired in the bottom of tower i0. Preferably pump I1 is placed downstream from cooler IS in order that the pump may act upon the cooled stream. In connection with this invention it has been found that the final extract phase produced by tower II and containing, as a result of the close fractionation therein, a concentration'of only the most soluble components of the fatty oil being treated is substantially as effective a solvent treating agent in tower It) as a stream of an equivalent volume of pure solvent. The oil components contained in the final extract phase liquid flowing through line l5 are present in such small concentration and are so highly soluble, particularly after the cooling step at I 6, that they have no appreciable effect on the action of the solvent portion of this liquid in treating the fresh fatty oil charged from line i8 in tower III.

This method of operation has the advantage that it permits limiting the vaporization of the solvent to the minimum quantity necessary for recirculation in relatively pure form to the bottom of tower ll through line 32, or to the quantity necessary to be recovered from liquid products withdrawn through lines 20, 28, 4i and 49.

In this m t od oi o eration two essentially separate solvent treatments are efiected by means of a single circulat ng stream of propane, represented by the propane introduced into reservoir 26 from line 25 and passed from reservoir 26 to tower it through line 32. This is an important advantage, since recovering the solvent by evaporation and condensation represents a substantial proport on of the operatvantage that it permits employing in tower Illsubstantially any desired solventroil ratio. Substantially all the solvent introduced into tower In from line l5 flows back again to tower ll through line iii. If valve 38 in line 36 is controlled to provide for removal of-a desired quantity of final extract phase for recovery of the final extract product fraction the quantity of final extract solution returned through line I5 for reuse in tower It may be varied at will, by control pump l1, without unduly disturbing the operation of the system.

According to an illustrative embodiment of the process of Fig. 1, volumes of fatty oil it introduced into tower l from line it in a unit of time are treated with 1800 volumes of liquefled propane introduced into tower 80 from line it. Tower 80. is operated to distribute 2 parts, by weight, of the oil to the first rafinate product fraction withdrawn through line 20. The

remainder ofthe fatty oil and substantially all of the propane pass overhead through line i9 and are transferred directly to tower ii for further treatment. Into tower l I 1000 volumes of propane, from reservoir 26,. are introduced through line 32 to complete the stripping operation in that tower, as described above. Approximately 100 volumes of propane are withdrawn from tower II in the secondary raifinate'phase through line 44.. The remaining 2700 volumes of propane pass overhead in the'final extract phase through line 36. One-third of this final extract phase passes to vessel 31 for recovery of solvent and the finalextract product fraction of the oil. Two-thirds of the final extract fraction, containing 1800 volumes of propane, are returned to tower I 0 from line 36 by being diverted through line l5. The operation of tower H is controlled to include in the final extract fraction a proportion of the oil such that the amount recovered at 31 for withdrawal from the process through line M is equivalent to 1 part by weight of the 100 parts of oil charged to the process through line i8. Consequently, the 1800 volumes of propane returned to tower l0 through line I5 contain only 2 parts of oil, and this oil is combined with the oil extracted in tower I0 whereby the extract phase passing out of tower l0 through line l9 contains 100 parts of oil and approximately 1800 volumes of propane. In this example tower I0 is operated at a propane:oil ratio of approximately 18:1 whereas tower H is maintained at a propaneroil ratio of approximately :1. The 1000 volumes of propane charged into the bottom of tower II are recovered by vaporization at 31 and 45. The volumes of propane indicated in this example merely illustrate an approximate distribution of propane in the system and do not take into account the relatively small quantities of propane which are recovered in secondary recovery operations on the product fractions and small quantities of make-up propane which are introduced into reservoir 26 from line 59 to re place inevitable losses.

Since the oil contained in the solution flowing through line l5 represents a highly soluble small proportion of the fatty oil, and since the solubility of this small proportion of oil is greatly increased by the cooling step at IS, the proportion of oil in the solvent stream introduced,

into the bottom of tower Hifrom line H'rmay be substantially increased over that indicated'in the foregoing illustrative embodiment. However, best operation of the process involves controlling the operation of tower II to restrict the amount of oil included in the final extract phase. For this reason it is desirable to operate tower ll substantially without the return of external reflux oil through line 42, or with the smallest amount of external refluxing necessary to produce suitable rectification of the product oil fraction. Any product oil desired for rectification through line 42 must be carried overhead in solution through line 36. Increasing the quantity of oil in line 36 to provide reflux oil at 31 also involves a corresponding increase in the concentration of oil in the solution diverted from line 36 through line It. For example, if in the i2 foregoing illustrative embodiment it were desired to return a quantity of reflux oil to tower it through line 62 equivalent to the quantity of product oil withdrawn from the process through line Cl this would result in doubling the concentration of oil in the solution flowing through line 55.

In a further modification of the process of Fig. 1, the solvent stream flowing through line IE to the bottom of tower 80, may be supplemented by a small quantity of relatively pure solvent diverted from line 32 through line 60. In this operation it may be desirable to introduce the solution from line l5 into tower ill at a somewhat higher point, as through line iii.

For a specific example of the application of the improved process reference may be made to a refining treatment of a crude soybean oil having a fatty acid content of 0.23 per cent. This oil was charged continuously to an extraction and decolorizing tower similar in construetion and operation to tower l0 of Fig. 1 and subjected in that tower to operating conditions designed to produce a first rafilnate fraction containing 2.5 weight per cent of the charge oil.

This tower was heldunder a pressure of 585 p. s."i'., and temperatures of 168 F., 164 F., and 163. F. were maintained at the top, oil charge point, and bottom, respectively. The final extract phase produced in this tower was passed continuously to a second fractionating tower similar in construction and operation to tower II of Fig. 1. In this second tower the extract phase was subjected to treatment at substantially higher temperatures, and the tower was refluxed with a temperature gradient and by the return of ex ternal reflux oil. Fresh liquefied propane was introduced into the bottom of this second tower in a manner similar to the introduction of fresh of oil charged to the first tower.

propane into the bottom of tower ll of Fig. 1 from line 32. .The second fractionating tower was regulated as to operating conditions to produce a second rafiinate product in the bottom of the tower containing 95.5 weight per cent of the oil charged to the first fractionating tower. The second tower was held under a pressure of 590 p. s. i., and temperatures of 195 F., 181 F., and 169 F. were maintained at the top, oil charge point, and bottom, respectively. The fresh propane was charged to the bottom of the second tower at a rate of 3280 volumes per 100 volumes of oil charged to the first tower. The extract solution from the top of the first tower contained 2780 volumes of propane per 100 volumes Approximately 100 volumes of propane per 100 volumes of charge oil were included in the second extract phase withdrawn from the bottom of the second tower. The final extract solution withdrawn from the top of the second tower contained 5960 volumes of propane per 100 volumes of oil charged to the first tower. A portion of the final extract solution containing 3180 volumes of propane was diverted and treated to vaporize the propane and separate liquid oil for withdrawal as the final extract product and for return as refiux liquid to the top of the second tower. The remaining portion of the final extract phase from the top of the second tower, containing 2780 volumes of propane per 100-volumes of fresh charge oil, provided the solvent, stream introduced into the bottom of the first tower. The second fractionating tower was refluxed externally by the return of approximately 11 parts of oil per parts of fatty oil charged the first tower.

' 13 to the first tower, and the extract oil from the top of the second tower was withdrawn as product atthe rate of 2 parts by weight per 100 parts of oil charged to the first tower. This required operating the second tower to include in the final extract phase approximately 25 parts by weight'of oil per-100 parts of fatty oil charged to the first tower. Consequently, the solvent stream introduced into the bottom of the first tower contained approximately 12 parts of the final extract oil per 100 parts of oil charged to This operation produced a substantially refined soybean oil equivalent to 95.5 weight percent of the crude oil, of light color and containing only 0.09 per centfatty acids. The final extract product oil withdrawn from the top of the second tower contained 5.0 weight per cent fatty acids and was a concentration of sterols, tocopherols, andother similar constit-- uents of the soybean oil. Theflrst raflinate product withdrawn from the bottom of the first tower was a concentrationof the color bodies of the crude soybean oil and also contained phosphatides, such as lecithin, in high concentration. This operation thus produced, through the operation of essentially a single circulating stream of solvent, a separation of the crude soybean oil into three fractions representing a lecithin concentrate, a sterol and tocopherol concentrate, and a substantially refined oil of good color. I

The improved process also is applicable to the separation of a fatty oil into four fractions, as by the use of three fractionating towers. One embodiment of this modification is illustrated in Fig. 2 in which fractionating tower Illa is arranged to function substantially in the same manner as tower I of Fig. 1. In this modification the first fractionating tower Illa preferably is operated to separate as the first raflinate in the bottom of the tower a relatively small fraction, i. e. not more than about per cent, and preferably 5 per cent or less, of, the oil charged to the process through line I8a. This small fraction represents a concentration of the color bodies and other relatively insoluble components of the oil, and is withdrawn from the process through line 20a. The modification of Fig. 2 differs from that of Fig. 1 in that the extract oil withdrawn overhead from tower Illa through line l9a is subjected to a preliminary fractionation to produce an intermediate raflinate product, prior to being passed to tower Ila for the production of the small final extract fraction.

This intermediate fractionation of the extract oil from tower Illa is provided in tower 62, which is similar in construction and operation to towers Illa and Ila, being provided with means for promoting intimate contact of counter-flowing liquid phases and being provided with heating coils 63 for control of temperature and the maintenance of a temperature gradient. In Fig. 2

apparatus for supplying external reflux oil to towers lila, 62 and Ila has not been shown, for simplicity of presentation. It will be understood, however, that any or all fractionating towers of Fig. 2 may be'subjected to external refluxing in the manner described in connection with towers- Ill and II of Fig. 1.

In Fig. 2 the parts whose function and operation are generally similar to corresponding parts of Fig. 1 are indicated by similar reference numerals, with. the subscript a. The description of such parts in Fig. 1 applies also to the 14 corresponding parts of Fig. 2, except as modified in the description of Fig. 2.

In accordance with the modification of Fig. 2 the extract solution withdrawn from the top of tower .Ifla through line Illa is passed to an intermediate point of tower 62. Alternatively, all or a portion of the solution flowing through line I 9a may be diverted through line a, and heated to a substantially higher temperature by heating means 52a to effect the formation of separate liquid phases. The phases are separated in vessel ila and separate phases are withdrawn through lines 53a and 54a for separate introduction into tower '62 in the manner described in connection with the separate phases withdrawn from vessel SI of Fig. 1.

Tower 62 is operated to separate the oil in troduced therein into a relatively small intermediate rafllnate fraction representing a concentration of the more unsaturated components of the oil. For example, in the refining of soybean oil by the modification of Fig. 2, tower 62 may be operated to separate anintermediate raiflnate fraction representing 15 to 35 per cent of the oil charged to the process through line I8a. The intermediate rafilnate fraction thus producedhas an increased value as a drying oil and is of good color by reason of the removal of color bodies from the oil in tower Illa. Such a drying oil fraction separated from a crude soybean oil in the method of Fig. 2 has an iodine number of 145 to 155, while the remaining oil carried overhead in solution -in tower 62 has a substantially lower iodine number of 125 to 135.

Tower 52 is operated at temperatures intermediate to those imposed on tower Ma and tower Ila. and the tower mav be subjected to external refluxing if desired. The in ermediate rafiinate product is withdrawn from the bottom of tower 62 through line .64, which discharges into a separator 65. Pressure is released at valve 66 sufliciently to evaporate the solvent which separates from the remaining liquid in vessel 65. The solvent vapors pass overhead through line 61, which connects with solvent reservoir 26a. A cooler 21a is provided to' condense the solvent vapors prior to introduction of the solvent into vessel 26a. The intermediate extract fraction is withdrawn from the bottom of vessel through line 68 for further treatment for the recovery of the oil contained therein.

The extract solution is withdrawn from the top of tower 62 through line '69, which connects with a tower I la at an intermediate point. Tower Ila is operated substantially exactly in the manner described in connection with tower l I of Fig. 1,

to separate the oil introduced into tower Ila into a relatively large final raflinate product and a relatively small final extract product. The operaiing conditions for tower Ila ordinarily differ somewhat from those applied in tower I I in the two-zone process of Fig. 1, since the final extract fraction to be removed overhead in tower Ila ordinarily represents a larger proportion of the oil charged to tower Ila than the proportion of oil charged to tower II represented by the final extract product produced by that tower. Thus control of tower I la ordinarily is easier than control of tower II, since the ratio of the extract product to the rafflnate product is somewhat larger than in tower I I.

The rafilnate phase separated in the bottom of tower Ila is withdrawn through line 44a which 76 connects with a separating vessel 45a. Pressure asoasss is released by valve 46a whereby the solvent contained in thi rafiinate product islargely evaporated and separated overhead as a vapor in vessel 45a. The solvent vapors are returned for reuse through line 08a, which connects with line 01. The final rafinate product, produced in tower I la, is withdrawn from vessel 4511. through line 49a for further treatment, such as the removal of residual quantities of solvent, and other desired further refining steps. This product is, however, except for the presence of solvent, a substantially refined oil of good color in which the fatty acid content has been reduced to the amount which is readily removable by moderate steam stripping.

The final extract phase is withdrawn from the top of tower Ila through line 36a, which connects with separating vessel 31a, and is provided with a valve 38a and heating means 39a. This equipment i operated in the same manner as similar is connected with line 61 for recirculation of the solvent. The final extract product is withdrawn through line Ma for further treatment, such as the removal of residual quantities of solvent, and other desired refining steps. resents ahigh concentration of the fatty acid content of the fatty oil being treated, and also a high concentration of the sterol and tocopherol content of the fatty oil.

A portion of the final extract phase flowing through line 36a is diverted through line I5a, which is provided with cooling means Iliaand a pump Ila. Line I5a connects with tower Illa at a low point in order to supply to tower Illa a stream of solvent, in a manner analogous to the operation of line I5 and tower I in Fig. 1. A sufficient quantity of final extra-ct phase is diverted through line, Ia to provide a solvent stream for tower 62 also. The solvent stream for tower 62 is diverted from line I5a through line 69, which is provided with cooling means I0 and a pump II. Line 69 connects with tower 62 at a low point in order to supply the solvent stream to that tower in the manner described in connection with line l5 and tower I0 of Fig. 1. Line 69, cooling means I0, and pump II operate in a manner analogous to lin I5, cooling means I6, and pump II of Fig. 1.

According to an illustrative embodiment the process of Fig. 2, 100 volumes of fatty oil introduced into tower Illa from line I8a in a unit of time are treated with 1800 volumes of liquefied propane introduced into tower Illa from line I5a. Tower Illa is operated to distribute 2 parts of the fatty oil to the first rafiinate product withdrawn through line a. The remainder of the fatty oil tower 62 for further treatment. Into tower 62 1800 volumes of propane are introduced through line 69. Tower 62 is operated to separate an intermediate rafiinate fraction equivalent to parts of the oil charged to the process. This oil and about 30 volumes of propane are withdrawn from the process through line =64. The remainder of the oil introduced into tower 62, together with all the remainder of the propane, passes overhead and is introduced into tower Ila for treatment in the manner described. In tower Ila conditions are controlled to separate a final raflinate product comprising 66 parts of the oil charged to the process. This oil and approximately 70 volumes of propane are withdrawn from the processthrough This fraction rept 16 line a. 01' the 3600 volumes of propane charged to tower 62 per parts of oil charged to the process through line I8a, approximately 30 vol= umes are withdrawn from the bottom and the remaining 3570 volumes are introduced into tower Ila through line 69'. Into the bottom of tower IIa approximately 1000 volumes of propane are introduced through line'32a, which connects the bottom of tower Ila with reservoir 26a. Of the total of 4570 volumes of propane thus charged to tower IIa approximately 70 volumes are withdrawn from the bottom with the raflinate. The remaining 4500 volumes pass overhead in the final extract phase through line 36a. A portion of this final extract phase containing 900 volumes of propane passes to vessel 31a for recovery of solvent and the final extract product. The remaining 3600 volumes of propane are diverted through line Hill, and of this quantity 1800 volumes pass through line 69 to the bottom of tower 62, while 1800 volumes are introduced into the bottom of tower Illa. Since the propane passed to vessel 31a contains approximately 2 parts of the oil as the final extract product the 3600 volumes of propane diverted through line I5a are accompanied by approximately 8 parts of fatty oil per 100 parts of oil charged to tower Illa. This fatty oil is equally distributed between streams of solvent passing to towers I0a and 62. ,Consequent-= ly in the above operation th overhead extract phase withdrawn from tower Illa through line I9a contains approximately 1800 volumes of propane and approximately 102 parts of the fatty oil per 100 parts of oil charge. After the separation treatment in tower 62 the extract phase passing overhead from that tower through line 69 contains approximately 3570 volumes of propane and 58 parts of oil per 100 parts of the fatty oil charged to the process.

In a further modification of the process of Fig. 2, the solvent stream flowing through line 69 to the bottom of tower 62 may be supplemented by a small quantity of relatively pure solvent diverted from line 32a through line I2. In this operation it may be desirable to introduce the solution from line '69 into tower 62 at a somewhat higher point.

In a further modification of the process of Fig. 2, the solvent stream flowing through line I5a to the bottom of tower Illa may be treated to remove free fatty acids. In this operation all or a portion of the liquids flowing through line I5a are diverted through line 13. Alkali is introduced through line 14 and the resulting mixture passes through mixer I5 to a settler 16. In settler 1B the soaps formed are permitted to settle and are drawn oil through line 11, while the resulting neutral solution is returned to line Ilia through line I8. This modification has the advantage that the accumulation of fatty acids in the system is reduced and any soaps which are not removed by settling at 16 are subjected to two precipitation treatments in towers Illa and I52 prior to the final separation of the raffinate fraction of the oil in tower Ila, which may be intended for use as an edible oil. A

A further modification of the application of the process to the continuous separation of the fatty oil into four fractions by the use of three fractionating towers is illustrated in Fig. 3. In this modification the first fractionating tower Illb preferably is operated to separate as the first rafiinate in the bottom of the tower a relatively large minor portion of the fatty oil. For example, in the treatment of soybean oil charged to tower lob through line lab operating conditions are controlled toseparate a rafflnate comprising a minor portion of the fatty oil charged to the tower and representing a concentration of the unsaturated components of the fatty oil, as well as a concentration of color bodies and other relatively insoluble components of the oil. In this modification tower Hlb is operated under conditions effective to produce a railinate comprising oil equivalent to 15 to 45 per cent of th fatty oil charged to tower I0, preferably 25 to 35 per cent. Tower Illb is constructed and arranged to function sub.- stantially in the same manner as tower I of Fig. 1. Tower ND is constructed and arranged to function substantially in the same manner as tower I I of Fig. 1 and tower Ila of Fig. 2. The operation of tower Ilb closely resembles that of tower Ila, since the extract oil treated in tower I Ib represents a fraction of the fatty oil generally similar to the fraction treated in tower I la of Fig. 2. The modification of Fig. 3 differs from that of Fig. l largely in that the relatively large minor fraction of the fatty oil separated as raffinate in tower I0!) is further treated in tower 19 to extract most of this railinate in an intermediate extract product oil of good color and good drying qualities, while concentrating the color bodies and I other less soluble components in a relatively small ramnate product separated in the bottom of tower I9. Tower i9 is similar in construction and arrangement to the other fractionating towers, be ing arranged to effect close fractionation of the oil into the desired fractions. Tower 19, like the other towers described, is substantially elongated vertically and is provided with contact means to facilitate contact of the counter-flowing liquid phases. Tower 19 is provided with heating coils 80 for control of temperature and the maintenance of a temperature gradient, and may also be provided with means for effecting external refluxing of the tower. In Fig. 3 apparatus for supply ing external reflux oil to towers IIlb, iIb and 19 has been omitted, for simplicity of presentation. It is to be'understood, however, that any or all of these towers may be subjected to external refluxing in the manner described in connection with towers it and l i of Fig. 1.

In Fig. 3 the parts whose function and operation are generally similar to corresponding parts of Fig. 1 are indicated by similar reference numerals, with the subscript b. It will be understood that the description of such parts given above in connection with Fig. 1 applies also to similarly numbered parts of Fig. 3, except as modified by the description of Fig. 3.

The relatively large raifinate, comprising a minor fraction of the fatty oil, which is collected in the bottom of tower It?) is withdrawn there from through line 20b, which connects with tower 19 at an intermediate point. A solvent stream is introduced into tower BS from line H, and this solvent stream flows upwardly in tower is in counter-current contact with the downfiowing oil phase, in the manner described above in connection with the other towers. Since tower i9 is provided to extract a major portion of the oil charged to the tower the operating temperature of tower l9 ordinarily is somewhat lower than that of tower Iflb. Ordinarily operating conditions in tower 19 are regulated to restrict the final railinate in this tower to less than 10 per cent, and preferably less than 5 per cent, of the fatty oil charged to the process through line tab. This minor fraction, representing a concentration of color bodies and other less soluble components of the fatty oil, is withdrawn from tower l9 througl line 82.

The extract phase formed in tower 19 is withdrawn overhead through line 83, which connect with separating vessel 84. Pressure on this extract phase is reduced at valve to eifect substantial evaporation of the solvent, heat beini supplied by heating means 86 to facilitate evapo' ration. The solvent vapors are separated in vessel 84 and withdrawn overhead through line 81 which connects with line 40b, whereby the solvent is conveyed back to solvent reservoir 26?: cooling means 21b being provided in line 40b tr condense the solvent vapors. The liquid separated in vessel 84 is withdrawn through line 8! for further treatment, such as the removal 01 residual quantities of solvent, and other desired refining steps. This fraction is a drying oil oi ood color.

The extract phase produced in tower I0!) is withdrawn overhead through line I9b, which connccts with tower Ilb at an intermediate poini thereof. In tower I Ib the extract oil is subjected to further fractionation treatment with relatively pure solvent introduced into the bottom of tower IIb through line 3212 from reservoir 26!). Tower III) is operated to separate the extract oil introduced into the tower into a relatively large intermediate fraction as a rafiinate product and a relatively small final extract fraction comprising a concentration of the most soluble components of the fatty oil. The operation of tower lib is generally similar to that of tower II and tower Ila, and the details or" operation described in connection with those towers apply also to the operation of tower Ill). The relatively large raiiinate produced in tower III) is withdrawn from the bottom thereof through line Mb, which connects with a separating vessel 45b. Pressure is reduced at valve 461; whereby there is substantial evaporation of solvent which passes overhead in vessel @512 through line 48b to line 40b. The liquid separated in vesse1 45b is withdrawn through line 59b for further treatment to recover the substantially refined fraction of light color and low fatty acid content.

The final extract phase formed in tower it?) is withdrawn overhead through line 36b, which con= nects with separating vessel 37b. Pressure is re leased at valve 38b and heat is supplied at heating means 391) to effect substantial evaporation of the solvent which passes overhead in vessel 31b through line 40b. A relatively small final extract fraction is withdrawn from the process from vessel 3th through line 4Ib. This fraction represents a concentration of fatty acids of the fatty oil and also a concentration of the tocopherol and sterol content of the oil.

A portion of the solvent phase flowing through. line 36b is diverted therefrom through line we for transfer to the bottom of tower I 0b as the solvent stream therefor. Line I52) is provided with cooling means Ifib and a pump llb whereby it functions in substantially exactly the same manner as line I5 of Fig. 1 and line Ida of Fig. 2. Another portion of the solvent phase flowing through line 36b-is diverted through line 85 in order to supply a portion of the final extract phase to the bottom of tower I9 as the solvent stream therefor. 'Line M is provided with cooling means 8% and a pump to effect transfer of the extract phase into tower 19 and to cool the extract phase to the lower temperature desired in the bottom of tower I9.

According to an illustrative embodiment of the process of Fig. 3, 100 volumes of fatty oil are charged into the system through line l8b in a unit of time, while 1100 volumes of liquefied propane are introduced into the bottom of tower llb through line 32b. Extract solution from the top of tower llb is transferred through line lb to the bottom of tower lllb at the rate of 1500 volumes of propane per 100 volumes of charge 011. Tower lDb is operated to distribute 30 parts of the oil contained therein to a first raffinate which separates in the bottom of tower lllb. This rafilnate fraction, containing about 30 volumes of propane, is transferred through line 20b to tower 19. Extract solution from the top of tower llb is introduced, through lines 36b and 8 lb, into the bottom of tower 19 at the rate of 500 volumes of propane per 100 volumes of oil charged to the process through line l8b. Tower 19 is operated to separate a final rafiinate fraction containing 2 parts of the fatty oil which is withdrawn from the bottom of tower 19 through line 82. Substantially all the propane introduced into tower 19 passes overhead through line 83, and these 530 volumes of propane are recovered at 84 for recirculation to reservoir 26b. The 1500 volumes of propane introduced into the bottom of tower lllb from line l5b pass entirely to the extract phase withdrawn overhead, except for approximately 30 volumes which are included in the rafiinate solution withdrawn through line 20b. The 1470 volumes of propane contained in the extract phase flowing from the top of tower lllb through line I 9b are all introduced into tower llb. The sum of this volume plus the volume of propane introduced into the bottom of tower l lb from line 32b is 2570. Tower llb is controlled to separate a rafiinate fraction equivalent to approximately 66 parts of fatty oil per 100 parts of fatty oil charged to the process through line l8b. This raflinate solution withdrawn from the bottom of tower l lb through line 44b also contains approximately 70 volumes of propane. The remainder of the propane introduced into tower llb, 2500 volumes, is included in the extract solution withdrawn from the top of tower llb through line 36b. As has been described, approximately three-fifths of this extract phase is diverted to tower lllb through line I51), and one-fifth is diverted to tower 19 through line 8|. The remaining one-fifth of the extract phase withdrawn from tower l lb is passed to vessel 31b for separation of the solvent from the product oil. The operating conditions of tower I lb are controlled whereby approximately 2 parts by weight of the fatty oil, per 100 parts of fatty oil charged to the process through line l8b, are recovered from solvent at 31b. Consequently, the solvent stream passed to tower lllb through line 85b contains Gparts of fatty oil, while the stream flowing through line 8i contains 2 parts of fatty oil. Consequently, the extract phase flowing through line l9b to tower llb contains 76 parts by weight of fatty oil per 100 parts of oil charged to the process through line 89b.

In accordance with one modification of the method of Fig. 3, all or a portion of the solvent stream for tower 59 may be provided in an alternative manner. In this modification a portion of the extract phase flowing through line l9?) from tower lllb to tower llb is diverted through line 9i, which connects with a phase separating vessel 92. The extract phase material flowing through line 9i is heated by heating means 93 to a temperature sufiiciently high to effect precipi tation of the maximum possible proportion of the oil content thereof as a separate liquid phase.

. tion of tocopherols, sterols, and fatty acids.

- process of the invention is applicable also to the The precipitated material settles out as a lower liquid phase in vessel 92. This material is withdrawn from the bottom of vessel 92 through line 94 which discharges into line l9b whereby the lower phase material separated in vessel 92 is subjected to fractionating treatment in tower l lb in the manner described. Cooling means 95 may be provided in line 94 to adjust the temperature. The upper phase is withdrawn overhead from vessel 92 through line 96. Line 96 connects with line 8| to effect transfer of the overhead phase material from vessel 92 to the bottom of tower 19 as all or a portion of the solvent stream for that tower.

In accordance with a further modification of the process of Fig. 3, the solvent stream flowing to tower 19 through line 8l is treated to remove fatty acids therefrom. In this modification the solvent stream is diverted from line 8l through line 91. Alkali is introduced into line 91 from line 98 and the resulting mixture flows through line 91 and mixer 99 to a settler I00. In settler I00 the soaps are permitted to settle and are withdrawn through line llll. The neutralized solvent stream is then returned to line 8| through line 32. This modification has the advantage that the fatty acid content of the solvent, which might otherwise be included in the drying oil fraction, is removed prior to contactof the solvent with the oil treated in tower 19.

In any of the above-described methods of operating the process of Fig. 3, tower llb may be operated primarily to strip the raflinate product of the tower and produce a solvent stream at the top. In this operation no extract solution from tower llb passes to vessel 31b for separation of oil, and the light portion of the fatty oil is all incorporated in the extract product of tower 19, except for fatty acids removed at I00.

In the foregoing detailed description of the improved process reference has been made to the refining of vegetable oils such as soybean oil, in which the final extract fraction is a concentra- The treatment of vitamin-containing fish oils to separate a small final extract which is a concentration of the vitamin content of the charge oil. In the treatment of a vitamin oil in the processing arrangement of Fig. 1, the oil may be treated in tower ID to separate a small rafiinate fraction which is a concentration of the color bodies, and the decolorized extract oil is then further treated in tower II to separate a small final extract fraction containing the vitamins in big-h concentration. The rafiinate fraction separated in tower H is a refined oil of good color which still may have suflicient vitamin potency for certain uses as a vitamin oil.

The processing arrangement of Fig. 1 also may be used in subjecting a vitamin oil to a two-stage concentrating treatment. In this arrangement tower l9 is operated under conditions effective to separate a raifinate comprising the bulk of the P oil. A relatively small extract fraction is then passed to tower ii for further concentration treatment to produce the final small extract. In this processing arrangement it may be desirable to operate tower ill to separate an extract fraction containing only a little more of the oil than is desired in the final fraction containing the vitamin concentrate. For example, tower 19 may be operated to separate a rafiinate containing 96 per cent of the oil. The 4 per cent extract oil from tower all is then fractionated in tower ll into approximately equal portions, the rafflnate fraction from tower ll constituting the vitamin concentrate. This method of operation is based on the fact that the concentration of the highly soluble stearin content of vitamin oils in the final V extract fraction makes it difiicult to produce concentrates of high potency in the final extract. In this operation, by careful regulation of the operation of tower i I, the vitamin content of the oil is largely concentrated in the raflinate withdrawn from the bottom of tower ll through line H. The oil fraction recovered overhead from tower II and withdrawn through line 4| may then be subjected to refrigeration to separate the stearin from any oil included in the extract fraction. The stearin separated in this manner may be washed by means of relatively cold solvent from reservoir 26, prior to passage of the solvent to tower ll through line 32, in order to recover and return to the system any vitamin-containing oil included in the final extract fraction from tower ll.

Any of these methods of treatment of fish oils by means of the processing arrangement of Fig. 1 may be carried out also in the processing arrangement of Fig. 2, with certain additional steps provided for by Fig. 2. For example, a fish body oil may be treated in accordance with the arrangement of Fig. 2 to separate a small color fraction at 20a, an intermediate drying oil fraction at 64, an intermediate edible oil fraction at a, and a vitamin fraction at Ma. Alternatively, towers 62 and Ma of Fig. 2 may be employed in a two-stage concentration treatment of decolorized extract oil from tower Illa, as described above in connection with Fig. 1.

The operating conditions and the material distributions described above in connection with the various modifications of the process illustrated by the drawings necessarily refer to conditions existing after equilibrium has been reached in the operation of the process. It. will be understood that any of the available operating expedients may be employed for reaching equilibrium conditions. For example, in starting up the system represented by Fig. 1, tower ll may be operated temporarily at a hig-her-than-normal top temperature until the oil recovered at 31 is of desired quality. Thereafter the temperature may be lowered gradually to increase the quantity of the oil distributed to the extract phase. Furthermore, all of the oil separated at 31 may be returned to the top of tower ll through line 42 until the quality of the oil separated at 31 is satisfactory. Similar starting-up procedures may be applied to the other systems of operation illustrated in the drawings.

I claim:

l. A method for refining a fatty oil which comprises introducing said oil into a solvent extraction zone wherein said oil is contacted with a solvent for said oil which solvent is relatively volatile having a critical temperature not substantially higher than 450 F., maintaining the temperature in said extraction zone above the temperature'of maximum solubility of the oil in the solvent and under a pressure effective to maintain the solvent substantially entirely in the liquid condition in the extraction zone, regulating the conditions of temperature and pressure in said extraction zone to form an extract phase containing a major proportion of said fatty oil and a raifinate phase containing a minor proportion of said fatty oil including a concentration of the color bodies of said oil. separately withdrawing said extract and rafllnate phases from said extraction zone, continuously passing a stream of said solvent in liquid condition upwardly in an elongated solvent fractionation zone from a lower solvent inlet to an upper extract phase outlet, introducing into said fractionation zone extract oil comprising at least a portion of the oil separated from said fatty oil by said extraction zone including at least a portion of the most soluble components of said fatty oil, introducing said extract oil into said fractionation zone and into contact with said solvent stream at a point below said extract phase outlet and substantially higher than said solvent inlet to form separate counter-flowing extract and raffinate phases, maintaining the lowest temperature in said fractionation zone above the temperature of maximum solubility of said extract oil in said solvent and applying suificient pressure to said fractionation zone to maintain the solvent therein substantially entirely in the liquid condition, regulating temperature and pressure and the solvent:oil ratio in said fractionation zone to form a raffinate phase in the bottom thereof comprising oil equivalent to at least a major portion of said extract oil charged to said fractionation zone and to form an extract phase containing a portion of the extract oil charged to the fractionation zone, separately withdrawing said extract and rafiinate phases from said fractionation zone, treating a portion of said lastmentioned withdrawn extract phase to recover solvent and a product oil fraction therefrom, segregating another portion of said last-mentioned withdrawn extract phase and adjusting the temperature and pressure thereof to a condition of greater solubility of said solvent and said fatty oil, and introducing said segregated portion of extract phase into said extraction zone to supply thereto at least a major portion of the solvent required in the said extraction treatment in said zone.

2. The method of claim 1 in which a liquefied normally gaseous solvent is employed.

3. The method of claim 1 in which liquefied propane is employed as the solvent.

4. The method of claim 1 in which the raffinate withdrawn from said extraction zone is limited to less than 10 weight per cent of the fatty oil, all the extract oil from the extraction zone is treated in the fractionation zone to form a raffinate phase therein containing oil equivalent to more than 80 weight per cent of the fatty oil, and less than 10 weight per cent of the fatty oil is recovered as a product oil fraction from the final extract phase formed in the fractionation zone.

5. The method of claim 1 wherein extract oil from the extraction zone is passed to the fractionation zone without substantial separation of accompanying solvent.

6. A method for refining crude soybean oil which comprises introducing said oil into a solvent extraction zone wherein saidoil is contacted with a solvent for said oil which solvent is rela-,- tively volatile having a critical temperature not substantially higher than 450 F., maintaining the temperature in said extraction zone above the temperature of maximum solubility of the oil in the solvent and under a pressure eifective to maintain the solvent substantially entirely in the liquid condition in the extraction zone, regulating the conditions of temperature and pressure in said extraction zone to form a rafiinate phase containing not more than about 5 weight per cent of the crude soybean oil chargedto the extraction zone and an extract phase containing the remainder of the crude soybean oil, separately withdrawing said extract and rafiinate phases from said extraction zone, continuously passing a stream of said solvent in liquid condition upwardly in an elongated solvent fractionation zone from a lower solvent inlet to an upper extract phase outlet, introducing the extract oil from the extraction zone into said fractionation zone and into contact with said solvent stream at a point below said extract phase outlet and substantially higher than said solvent inlet, maintaining the lowest temperature in said fractionation zone above the temperature of maximum solubility of said extract oil in said solvent and applying suiiicient pressure to said fractionation zone to maintain the solvent therein substantially entirely in the liquid condition and form separate counter-flowing extract and raifinate phases, regulating temperature and pressure and the solventzoil ratio in said fractionation zone to form a raflinate phase in the bottom thereof comprising oil equivalent to not less than about 93 weight per cent of the crude soybean oil charged to the extraction zone and to form an extract phase containing a portion of the extract oil charged to the fractionation zone, separately withdrawing said extract and rafiinate phases from said fractionation zone, treating a portion of said last-mentioned withdrawn extract phase to recover solvent and a product oil fraction therefrom, segregating another portion of said last-mentioned withdrawn extract phase and adjusting the temperature and pressure thereof to a condition of greater solubility of said solvent and said fatty oil, and introducing said segregated portion of extract phase into said extraction zone to supply thereto at least a major portion of the solvent required in the said extraction treatment in said zone.

7. A method for refining a fatty oil which comprises introducing said oil into a solvent extraction zone wherein said oil is contacted with a solvent for said oil which solvent is relatively volatile having a critical temperature not substantially higher than 450 F., maintaining the temperature in said extraction zone above the temperature of maximum solubility of the oil in the solvent and under a pressure effective to maintain the solvent substantially entirely in the liquid condition in the extraction zone, regulating the conditions of temperature and pressure in said extraction zone to form an extract phase containing a major proportion of said fatty oil and a rafiinate phase containing a minor proportion of said fatty oil including a concentration of color bodies of said oil, separately withdrawing said extract and raflinate phases from said extraction zone, continuously contacting extract oil from said extraction zone with another portion of said solvent in a second extraction zone at a temperature above the temperature of maximum solubility of the oil and the solvent to separate a second rafiinate phase equivalent to a minor proportion of the fatty oil charged to the first-mentioned extraction zone, separately withdrawing extract and rafiinate phases from said second extraction zone, continuously passing a stream of said solvent in liquid condition upwardly in an, elongated solvent fractionation zone from a lower solvent inlet to an upper extract phase outlet, introducing the extract oil from said second extraction zone into said fractionation zone and into contact with said solvent stream at a point below said extract phase outlet and substantially higher than said solvent inlet, maintaining the lowest temperature in said fractionation zone above the temperature of 5 maximum solubility of said extract oil in said solvent and applying pressure to said fractionation zone to maintain the solvent therein substantially entirely in the liquid condition and form separate counter-flowing extract and ramnate phases, regulating temperature and pressure and the solventzoll ratio in said fractionation zone to form a raiilnate phase in the bottom thereof comprising oil equivalent to a major proportion of said fatty oil charged to said first-mentioned extraction zone and to form an extract phase containing a portion of the extract oil charged to the fractionation zone, separately withdrawing said extract and rafiinate phases from said fractionation zone, treating a portion of said last-mentioned withdrawn extract phase to recover solvent and a product oil fraction therefrom, segregating two other portions of said last-mentioned withdrawn extract phase and adjusting the temperature and pressure thereof to conditions of greater solubility of said solvent and said fatty oil, and introducing said segregated portions of extract phase into said first-mentioned and said second extraction zones to supply to each zone at least a major portion of the solvent required in the said extraction treatment in. each zone.

8. A method for refining a fatty oil which comprises introducing said oil into a solvent extraction zone wherein said oil is contacted with a solvent for said oil which solvent is relatively volatile having a critical temperature not substantially higher than 450 II, maintaining the temperature in said extraction zone above the temperature of maximum solubility of the oil in the solvent and under a pressure effective to maintain the solvent substantially entirely in the liquid condition in the extraction zone, reguluting the conditions of temperature and pressure in said extraction zone to form an extract phase containing a major proportion of said fatty oil and a raflinate phase containing a minor proportion of said fatty oil, separately withdrawing said extract and raftinate phases from said extraction zone, continuously contacting rafiinate oil from said extraction zone with another portion of said solvent in a second extraction zone at a temperature above the temperature of maximum solubility of the oil and the solvent to separate a final rafiinate product containing a minor proportion of the oil introduced into said second extraction zone and an intermediate extract phase containing a major proportion of the oil introduced into said second extraction zone, separately withdrawing said extract and rafiinate 60 phases from said second extraction zone, continuously passing a stream of said solvent in liquid condition upwardly in an elongated solvent fractionation zone from a lower solvent inlet to an upper extract phase outlet, introducing the 65 extract oil from said first-mentioned extraction zone into said fractionation zone and into contact with said solvent stream at a point below said extract phase outlet and substantially higher than said solvent inlet, maintaining the lowest 70 temperature in said fractionation zone above the temperature of maximum solubility of said extract oil in said solvent and applying sufiicient pressure to said fractionation zone to maintain the solvent therein substantially entirely in the is liquid condition and to form separate counter- ,ratio in said fractionation zone to form a raffinate phase in the bottom thereof comprising oil equivalent to a major portion of said fatty oil charged to said first-mentioned extraction zone and to form an extract phase containing a portion of the extract oil charged to the fractionation zone, separately withdrawing said extract and rafllnate phases from said fractionation zone. treating a portion of said last-mentioned withdrawn extract phase to recover solvent and a product 011 fraction therefrom, segregating two other portions of said lastmentioned withdrawn extract phaseand adjusting the temperature and pressure thereof to conditions of greater solubility of said solvent and said fatty oil, introducing said segregated portions of extract phase into said first-mentioned and said second extraction zones to supply to each zone at least a major portion of the solvent required in said extraction treatment in each zone.

9. In the refining of a fatty oil by a series of at least two paracritical fractlonations with a low-boiling solvent having a critical temperature not substantially higher than 450 F., the improvement which includesthe steps of: subjecting said fatty oil to a first fractionation into primary extract and raffinate phases in a first fractionation zone with a solvent comprised principally of said low-boiling solvent under temperatures in the paracritical range and under liquefying pressure; separately withdrawing said primary extract and rafilnate phases and subjecting at least part of said primary extract to a subsequent fractionation into secondary extract and raffinate phases in a separate fractionation zone with additional solvent, said solvent being comprised principally of said low-boiling solvent, and said subsequent fractionation being carried out at paracritical temperatures higher than those prevailing in the first fractionation zone; separately withdrawing said secondary extract and rafiinate phases from said separate fractionation zone; cooling at least a substantial part of said secondary extract phase and pumping said cooled secondary extract phase into said first fractionation zone to serve as solvent therein.

10. In the refining of a fatty oil by a series of at least two paracritical fractionations with a low-boiling solvent having a critical temperature not substantially higher than 450 F., the improvement which includes the steps of: subjecting said fatty oil to a first fractionation into primary extract and raffinate phases in a first fractionation zone with a solvent comprised principally of said low-boiling solvent under temperatures in the paracritical range and under liquefying pressure; separately withdrawing said primary extract and railinate phases and subjecting at least part of said primary extract to a subsequent fractionation into secondary extract and rafiinate phases in' a separate fractionation zone with additional solvent, said solvent being comprised principally of said low-boiling solvent, and said subsequent fractionation being carried out at a pressure sufficient to maintain said solventoil mixture in liquid condition but substantially lower than the pressure prevailing in said first fractionation zone; separately withdrawing said secondary extract and raffinate phases from said separate fractionation zone; and pumping at least a substantial part of said secondary extract phase into said first fractionation zone to serve as solvent therein.

11. In the refining of afatty oil by a series of at least two paracritical fractionations with a low-boiling solvent having a critical temperature not substantially higher than 450 F., each of said fractionations being carried out in a vertically extended fractionation zone with an extract phase outlet at the upper end, a raifinate phase outlet and solvent inlet near the lower end, and a charge oil inlet intermediate said ends, the improvement which includes the steps of: charging said fatty oil and a solvent comprised principally of said low-boiling solvent to a first vertically extended fractionation zone and regulating the conditions of temperature and pressure therein to form a primary extract phase containing a major proportion of said fatty oil and a primary raffinate phase containing a minor proportion of said fatty oil including a concentration of color bodies of said oil; separately with drawing said extract and raffinate phases from said extract and rafiinate phase outlets respectively and charging to a second vertically extended fractionation zone a charge derived from said primary extract phase; countercurrently contacting said charge with said low-boiling solvent in said second zone and regulating the conditions of temperature and pressure therein to reject a major proportion of the oil in said charge into a secondary rafiinate phase and to form an upfiowing extract phase containing a relatively small proportion of oil; separately withdrawing said secondary extract and raffinate phases, from said second fractionation zone; diverting at least a major proportion of said secondary extract phase and adjusting the temperature and pressure of said diverted portion to a condition of greater solubility of said lowboiling solvent and said fatty oil; and introducing said diverted portion into the lower portion of said primary fractionation zone to supply thereto at least a major portion of solvent required in said zone.

12. A method as described in claim 11 in which the maximum temperature in the second vertically extended fractionation zone is substantially higher than the maximum temperature in the first fractionation zone and in which the diverted portion of the secondary extract phase is cooled to a temperature not higher than the lower of said temperatures.

13. A method as described in claim 11 in which said primary extract phase is treated to separate solvent therefrom and a relatively solvent-free primary extract oil comprises the charge in said secondary vertically extended fractionation zone.

14. A method as described in claim 11 in which said primary extract phase is separated into light and heavy components by heating to a higher temperature Within the paracritical range and said components are charged to said second vertically extended fractionation zone at vertically spaced inlets, the light component being introduced at the higher inlet.

15. A method as described in claim 11 in which said diverted portion of said secondary extract phase is pumped into the lower portion of said first fractionation zone at a rate which is varied to permit the constant removal of a desired quantity of product from the undiverted portion of said secondary extract phase.

16. A method as described in claim 11 in which the upfiowing solvent in said first vertically extended fractionation zone is comprised in part 27 of said low-boiling solvent of said solvent inlet at said lower end of first fractionation zone; and in part of said diverted portion of said secondary extract phase introduced into said first zone through an inlet located substantially above said 5 solvent inlet but below said fatty oil inlet.

GEORGEIH. PALMER.

28 nmmmons 0mm The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,118,454 Schaafsma May 24, 1938 2,394,968 Van Orden Feb. 12, 1946 2,139,392 Tijmstra Dec. 6, 1938 

1. A METHOD FOR REFINING A FATTY OIL WHICH COMPRISES INTRODUCING SAID OIL INTO A SOLVENT EXTRACTION ZONE WHEREIN SAID OIL IS CONTACTED WITH A SOLVENT FOR SAID OIL WHICH SOLVENT IS RELATIVELY VOLATILE HAVING A CRITICAL TEMPERATURE NOT SUBSTANTIALLY HIGHER THAN 450*F., MAINTAINING THE TEMPERATURE IN SAID EXTRACTION ZONE ABOVE THE TEMPERATURE OF MAXIMUM SOLUBILITY OF THE OIL IN THE SOLVENT AND UNDER A PRESSURE EFFECTIVE TO MAINTAIN THE SOLVENT SUBSTANTIALLY ENTIRELY IN THE LIQUID CONDITION IN THE EXTRACTION ZONE, REGULATING THE CONDITIONS OF TEMPERATURE AND PRESSURE IN SAID EXTRACTION ZONE TO FORM AN EXTRACT PHASE CONTAINING A MAJOR PROPORTION OF SAID FATTY OIL AND A RAFFINATE PHASE CONTAINING A MINOR PROPORTION OF SAID FATTY OIL INCLUDING A CONCENTRATION OF THE COLOR BODIES OF SAID OIL, SEPARATELY WITHDRAWING SAID EXTRACT AND RAFFINATE PHASES FROM SAID EXTRACTION ZONE, CONTINUOUSLY PASSING A STREAM OF SAID SOLVENT IN LIQUID CONDITION UPWARDLY IN AN ELONGATED SOLVENT FRACTIONATION ZONE FROM A LOWER SOLVENT INLET TO AN UPPER EXTRACT PHASE OUTLET, INTRODUCING INTO SAID FRACTIONATION ZONE EXTRACT OIL COMPRISING AT LEAST A PORTION OF THE OIL SPEARATED FROM SAID FATTY OIL BY SAID EXTRACTION ZONE INCLUDING AT LEAST A PORTION OF THE MOST SOLUBLE COMPONENTS OF SAID FATTY OIL, INTRODUCING SAID EXTRACT OIL INTO SAID FRACTIONATION ZONE AND INTO CONTACT WITH SAID SOLVENT STREAM AT A POINT BELOW SAID EXTRACT PHASE OUTLET AND SUBSTANTIALLY HIGHER THAN SAID SOLVENT INLET TO FORM SEPARATE COUNTER-FLOWING EXTRACT AND RAFFINATE PHASES, MAINTAINING THE LOWEST TEMPERATURE IN SAID FRACTIONATION ZONE ABOVE THE TEMPERATURE OF MAXIMUM SOLUBILITY OF SAID EXTRACT OIL IN SAID SOLVENT AND APPLYING SUFFICIENT PRESSURE TO SAID FRACTIONATION ZONE TO MAINTAIN THE SOLVENT THEREIN SUBSTANTIALLY ENTIRELY IN THE LIQUID CONDITION, REGULATING TEMPERATURE AND PRESSURE AND THE SOLVENT:OIL RATIO IN SAID FRACTIONATION ZONE TO FORM A RAFFINATE PHASE IN THE BOTTOM THEREOF COMPRISING OIL EQUIVALENT TO AT LEAST A MAJOR PORTION OF SAID EXTRACT OIL CHARGED TO SAID FRACTIONATION ZONE AND TO FORM AN EXTRACT PHASE CONTAINING A PORTION OF THE EXTRACT OIL CHARGED TO THE FRACTIONATION ZONE, SEPARATELY WITHDRAWING SAID EXTRACT AND RAFFINATE PHASES FROM SAID FRACTIONATION ZONE, TREATING A PORTION OF SAID LASTMENTIONED WITHDRAWN EXTRACT PHASE TO RECOVER SOLVENT AND A PRODUCT OIL FRACTION THEREFROM, SEGREGATING ANOTHER PORTION OF SAID LAST-MENTIONED WITHDRAWN EXTRACT PHASE AND ADJUSTING THE TEMPERATURE AND PRESSURE THEREOF TO A CONDITION OF GREATER SOLUBILITY OF SAID SOLVENT AND SAID FATTY OIL, AND INTRODUCING SAID SEGREGATED PORTION OF EXTRACT PHASE INTO SAID EXTRACTION ZONE TO SUPPLY THERETO AT LEAST A MAJOR PORTION OF THE SOLVENT REQUIRED IN THE SAID EXTRACTION TREATMENT IN SAID ZONE. 